Low Fragmented Chromatin Concentration

Symptom

DNA concentration of fragmented chromatin preparation is below expected ranges (e.g., <100 µg/ml for HeLa cells, <20 µg/ml for brain tissue). Insufficient material for recommended 5-10 µg chromatin per IP reaction.

1. 1 Insufficient starting material: fewer cells or less tissue than protocol specification (e.g., <4×10⁶ HeLa cells or <25 mg tissue)
2. 2 Incomplete cell or tissue lysis during nuclear extraction step
3. 3 Enzymatic protocol: incomplete nuclear membrane disruption after micrococcal nuclease digestion
4. 4 Poor tissue disaggregation (especially brain tissue without Dounce homogenizer)

1. 1 Count cells accurately before crosslinking or weigh tissue precisely to ensure adequate starting material
2. 2 If concentration is near 50 µg/ml, add additional chromatin volume to reach 5-10 µg per IP and proceed
3. 3 Enzymatic protocol: visualize nuclei under microscope before and after sonication to confirm complete lysis
4. 4 Use Dounce homogenizer for brain tissue disaggregation; Medimachine inadequate for this tissue type
5. 5 Harvest more than 25 mg tissue per IP for low-yield tissue types (brain, heart: 2-5 µg per 25 mg)